The present invention relates to a method of filtering and mainly relates to a filtration device for removing objects of removal from fluids with which very minute objects of removal of mainly 0.15 xcexcm or less are contained in a colloidal solution (sol).
Presently, diminishing the amount of industrial waste, separate collection and recycling of industrial waste, and preventing release of industrial waste are considered to be ecologically-important topics and business issues as society moves towards the 21st Century. Some types of industrial waste comprise various types of fluids containing objects of removal; i.e., substances to be removed.
Such fluids are known by a variety of expressions, such as sewage, drainage, and effluent. Fluids, such as water or chemicals, containing substances that are objects of removal, shall be hereinafter referred to as xe2x80x9cwastewater.xe2x80x9d The objects of removal are eliminated from wastewater by an expensive filtration system or a similar system. Wastewater is thereby recycled as a clean fluid, and the removed objects or substances that cannot pass through the filtration system are disposed of as industrial waste. In particular, water is sent back to a natural setting, such as a river or sea, or recycled after being purified so as to meet environmental standards.
Adoption of such a filtration system is difficult because of costs incurred in constructing and running a filtration system, thus posing an environmental problem.
As can be seen from the above, wastewater treatment techniques are important in terms of recycling and preventing environmental contamination, and an immediate demand exists for a filtration system that incurs low initial and running costs.
By way of illustration, wastewater treatment as practiced in the field of semiconductors shall now be described. When a plate member formed, for example, from a metal, a semiconductor, or ceramic, is ground or abraded, an abrasion (or grinding) jig or the plate member is subject to a shower of a fluid, such as water, for preventing an increase in the temperature of the abrasion (or grinding) jig, which would otherwise be caused by friction, for improving lubricity, and for preventing adhesion of abrasion or grinding waste onto the plate member.
More specifically, in the process of dicing or back-grinding of plate-like semiconductor material; e.g., a semiconductor wafer, pure water is made to flow over the semiconductor wafer. In a dicing machine, a shower of pure water is made to flow over a semiconductor wafer, or pure water is squirted onto a dicing blade from a discharge nozzle in order to prevent an increase in the temperature of the blade or adhesion of dicing waste onto the semiconductor wafer. For the same reason, a flow of pure water is employed during an operation in which a semiconductor wafer is made thin by back-grinding.
Wastewater, which has mixed therein grinding or abrasion waste and is discharged from the dicing or back-grinding machine, is returned to a natural setting or recycled after having been purified through a filter. Alternatively, concentrated wastewater is recovered.
In a current process for manufacturing a semiconductor, wastewater, in which objects of removal (i.e., waste) primarily consisting of Si are mixed, is disposed of according to one of two methods; i.e., a coagulating sedimentation method and a method which employs a filter and a centrifugal separator in combination.
Under the coagulating sedimentation method, polyaluminum chloride (PAC) or aluminum sulfate (Al2(SO4)3) is mixed in the wastewater as a coagulant to generate a reaction product with Si and the wastewater is filtrated to remove this reaction product.
Under the method that employs a filter and a centrifugal separator in combination, the wastewater is filtrated, the concentrated wastewater is processed by the centrifugal separator to recover the silicon waste as sludge, and the clear water resulting from filtration of the wastewater is released to a natural setting or is recycled.
For example, as shown in FIG. 11, wastewater discharged during a dicing operation is collected into a raw water tank 201 and is sent by a pump 202 to a filtration unit 203. A ceramic-based or organic-based filter F is provided in filtration unit 203, and the filtrated water is delivered via a pipe 204 to a collected water tank 205 for recycling. Alternatively, the filtrated water is released to a natural setting.
In filtration unit 203, since clogging of filter F occurs, washing is carried out periodically. For example, a valve B1 connected to raw water tank 201 is closed, a valve B3 and a valve B2, for delivering washing water from the raw water tank are opened, and filter F is cleaned by a reverse flow of water from collected water tank 205. The resultant wastewater containing a high concentration of Si waste is returned to raw water tank 201. Also, the concentrated water in a concentrated water tank 206 is transported via a pump 308 to centrifugal separator 209 and is thereby separated into sludge and separated fluid. The sludge comprising Si waste is collected into a sludge recovery tank 210 and the separated fluid is collected into a separated-fluid tank 211. After further accumulation of the separated fluid, the wastewater in separated-fluid tank 211 is transported to raw water tank 201 via pump 212.
These methods have also been employed for the recovery of waste resulting from grinding or abrasion of a solid or plate-like member formed essentially from a metal material, such as Cu, Fe, Al, etc., or from grinding or abrasion of a solid or plate-like member formed from ceramic or other inorganic material.
Chemical-mechanical polishing (CMP) has come to be employed as a new semiconductor processing technology.
This CMP technique enables
(1) the realization of smooth device surface shapes; and
(2) the realization of structures with embedded materials that differ from the substrate.
With regard to (1) above, fine patterns are formed precisely using lithography techniques. The combined use of techniques for affixing Si wafers enables materialization of three-dimensional IC""s.
With (2), embedded structures are made possible. Since priorly, a technique of embedding tungsten (W) has been employed in multilayer wiring of IC""s. With this technique, W is embedded by a CVD method in a trench of an interlayer film and the surface is made smooth by etching back. However, smoothing by CMP has come to be employed recently. Other examples of application of this embedding technique include damascene processes and element separation.
Such CMP techniques and applications are described in detail in xe2x80x9cScience of CMP,xe2x80x9d published by Science Forum Co., Ltd.
A mechanism for a CMP process shall now be described briefly. As shown in FIG. 12, a semiconductor wafer 252 is placed on an abrasive cloth 251 placed over a rotary table 250, and irregularities of the wafer 252 surface are eliminated by performing lapping, polishing, and chemical etching while pouring on an abrasive (slurry) 253. Smoothing is achieved by chemical reactions induced by a solvent included in abrasive 253 and by mechanical abrasive actions of the abrasive cloth and the abrasive grains in the abrasive. Foamed polyurethane or non-woven fabric, etc., is used, for example, as abrasive cloth 251. The abrasive has abrasive grains of silica, alumina, etc., mixed in water containing a pH regulator and is generally referred to as slurry. Lapping is performed while pouring on this slurry 253 and applying pressure onto abrasive cloth 251 while rotating wafer 252. A dressing part 254, maintains the abrading ability of abrasive cloth 251 and constantly keeps the surface of abrasive cloth 251 in a dressed condition. Numerals 202, 208, and 212 indicate motors and 255 to 257 indicate belts.
The above-described mechanism is arranged as a system as shown for example in FIG. 13. This system largely comprises a wafer cassette loading/unloading station 260, wafer transfer mechanism part 261, the abrasive mechanism part 262, which is described using FIG. 12, a wafer cleaning mechanism part 263, and a system controller for controlling these parts.
A cassette 264 having wafers stored therein is placed in wafer cassette loading/unloading station 260, and a wafer is taken out of cassette 264. In the wafer transfer mechanism part 261, the wafer is retained, for example, by a manipulator 265, and is placed on rotary table 250 disposed in abrasive mechanism part 262. The wafer is then smoothed by the CMP technique. After smoothing of the wafer has been completed, the wafer is transported by manipulator 266 to wafer cleaning mechanism part 263 wherein the slurry is cleaned off of the wafer. The washed wafer is then housed in wafer cassette 266.
The amount of slurry used for one abrasion process is about 500 cc to 1 liter/wafer. Also, pure water is made to flow in the above-described abrasive mechanism part 262 and wafer cleaning mechanism part 263. Since the resulting wastewater is merged in the final stage at a drain, about 5 to 10 liters/wafer of wastewater flows out during a single smoothing operation. In the case of producing, for example, a three-layer-metal wafer, about seven smoothing operations are required for smoothing the metal and interlayer dielectric films. Thus, wastewater of an amount of seven times the 5 to 10 liters is discharged for producing of a single wafer.
It can thus be understood that the use of a CMP machine involves discharge of a considerable amount of slurry diluted with pure water.
Such wastewater has conventionally been by a coagulating sedimentation method.
However, chemicals are used as coagulants in a coagulating sedimentation method. Specifying the amounts of chemicals that will react completely is very difficult, and hence excess amounts of chemicals are loaded and unreacted chemicals remain. Oppositely, if the amounts of chemicals are low, not all of the objects of removal will coagulate and settle and some of the objects of removal will thus remain unseparated. Especially in a case where excess amounts of chemicals are used, chemicals will remain in a supernatant liquid, and with regard to recycling, such a supernatant liquid could not be recycled for use in applications in which chemical reactions must be avoided since the chemicals remain in the liquid even after passage through a filter.
Also, floc, which is a reaction product of a chemical and objects of removal, is generated in the form of a tuft-like suspended solid. Production of such floc is achieved under strict pH conditions and requires an agitator, a pH measurement instrument, a coagulant injection apparatus, and control equipment for controlling these components. Also, stable sedimentation of floc requires a large-size precipitation tank. For example, for a wastewater treatment capacity of 3 cubic meters (m3)/hour, a precipitation tank with a diameter of 3 meters and a depth of about 4 meters (i.e., a precipitation tank with a capacity of about 15 tons) is required. As a result, the entire system will be a large-scale system requiring floor space of about 11 metersxc3x9711 meters.
Furthermore, some of the floc float on the surface without settling to the bottom of the precipitation tank and such floc may flow out of the precipitation tank. The recovery of all of the floc is thus difficult. In short, the known filtration system suffers such problems as large facility size, high initial costs required by the system, difficulties in recycling water, and high running costs incurred by use of chemicals.
On the other hand, with a method, such as that shown in FIG. 13, which employs a filter having a filtering capacity of 5 cubic meters (m3)/hour and a centrifugal separator in combination, recycling water becomes possible due to the use of a filter F (which is called a UF module and comprises polysulfone fibers or a ceramic filter) in filtration unit 203. However, filtration unit 203 is equipped with four filters F and, in view of the life of the filters F, the high-priced filters F, costing about 500,000 yen each, had to be replaced at least once a year. Furthermore, since filters F are to be used with a pressure filtration method, clogging of the filters placed a large motor load and pump 202 thus had to be high capacity. Also, of the wastewater passing through filter F, about two-thirds is returned to raw water tank 201. Furthermore, wastewater containing objects of removal is transported by pump 202, causing the interior wall of pump 202 to be scraped by the objects of removal and thus greatly shortening the life of pump 202.
To summarize the above, the known filtration system suffers high running costs, specifically, the cost of electricity consumed by the motor and expenditures required for replacing pump P and filters F.
Furthermore, in comparison to a dicing process, an incomparable amount of wastewater is discharged during a CMP process. A slurry is distributed in the form of a colloid in a fluid and does not precipitate readily due to Brownian motion. Moreover, the abrasive grains mixed in the slurry are very minute and comprise grains with particle diameters of 10 to 200 nm. When a slurry comprising such fine abrasive grains is filtrated through a filter, the abrasive grains enter the pores of the filter and cause clogging immediately and frequently, thus making treatment of a large amount of wastewater impossible.
As can be understood from the foregoing description, in order to eliminate maximal amounts of substances harmful to the global environment and recycle filtrated fluids or separated objects of removal, various devices had to be added to the wastewater filtration apparatus, thus making the system large in scale and leading to enormous initial costs and running costs. Known sewage treatment apparatuses were therefore systems that could not be employed.
The present invention has been conceived in view of the foregoing problems and is aimed at providing a filtration device comprising a tank which contains a fluid with objects of removal in the form of a colloidal solution. A filtration unit is formed of a first filter, which is immersed inside the above-mentioned tank. A second filter, comprising a gel film that is adsorbed onto the surface of the first filter, is also provided. A pump is provided for suctioning the above-mentioned fluid via a first pipe connected to the above-mentioned filtration unit. A second pipe is provided for removing filtrated fluid from the above-mentioned pump out to the exterior of the above-mentioned tank. The above-mentioned objects of removal in the above-mentioned fluid are concentrated in the above-mentioned tank.
The present invention is also aimed at providing a filtration device, wherein a gel film formed from the objects of removal is used as the second filter.
The present invention is also aimed at providing a filtration device, wherein the above-mentioned filtration unit comprises a frame, the above-mentioned first filter, which has the surroundings thereof supported by the above-mentioned frame, and the above-mentioned second filter, which is adsorbed onto the surface of the above-mentioned first filter.
The present invention is also aimed at providing a filtration device, wherein the above-mentioned filtration unit has two of the above-mentioned first filters disposed on the respective sides of the above-mentioned frame, a hollow part is formed between the above-mentioned frame and the above-mentioned first filters, the above-mentioned first pipe is connected to an upper part of the above-mentioned frame, and filtrated fluid is suctioned by the above-mentioned pump from the above-mentioned hollow part.
The present invention is also aimed at providing a filtration device, wherein the above-mentioned filtration unit comprises: the above-mentioned frame; a spacer provided with a plurality of holes; the above-mentioned first filter, which covers the above-mentioned spacer; and the above-mentioned second filter, which is adsorbed onto the surface of the above-mentioned first filter; and the above-mentioned spacer provides support when the above-mentioned first filter depresses inwards when suction is applied.
The present invention is also aimed at providing a filtration device, wherein the above-mentioned first filter is formed of a polyolefin-based polymer and the filter pores are larger than the diameters of the above-mentioned objects of removal.
The present invention is also aimed at providing a filtration device, wherein a plurality of the above-mentioned filtration units are disposed vertically and in a spaced manner in the above-mentioned fluid.
The present invention is furthermore aimed at providing a filtration device, wherein an aeration pipe is disposed at a bottom part of the above-mentioned tank and bubbles generated from the above-mentioned aeration pipe rise along the surface of the above-mentioned filtration unit to cause a parallel flow of the above-mentioned fluid along the above-mentioned filtration unit.
The present invention is furthermore aimed at providing a filtration device, wherein the above-mentioned pump is a compact, low power consumption pump that realizes weak suction pressure.
The present invention is furthermore aimed at providing a filtration device, wherein the above-mentioned first pipe is provided with a pressure gauge for measuring the suction pressure of the above-mentioned filtration unit.
The present invention is furthermore aimed at providing a filtration device, wherein a flow meter is inserted inside the above-mentioned second pipe and the suction pressure of the above-mentioned pump is controlled so as to keep the filtration flow rate measured by the above-mentioned flow meter fixed.
The present invention is furthermore aimed at providing a filtration device, wherein the above-mentioned second pipe is provided with an optical sensor at an end part thereof and is branched into a third pipe for taking filtrated fluid out to the exterior of the above-mentioned tank and a fourth pipe that returns filtrated fluid to the above-mentioned tank. Switching between the above-mentioned third and fourth pipes is carried out in accordance with the optical transmittance detected by the above-mentioned optical sensor.
The present invention is furthermore aimed at providing a filtration device, wherein an auxiliary tank, connected to the above-mentioned first pipe, is provided and filtrated fluid is collected in the above-mentioned auxiliary tank.
The present invention is furthermore aimed at providing a filtration device, wherein the above-mentioned objects of removal comprise a CMP slurry.
The present invention is furthermore aimed at providing a filtration device comprising: a tank, containing a fluid that contains objects of removal in the form of a colloidal solution; a filtration unit, formed of a first filter, which is immersed inside the above-mentioned tank, and a second filter, comprising a gel film that is adsorbed onto the surface of the first filter; a pump, for suctioning the above-mentioned fluid via a first pipe connected to the above-mentioned filtration unit; a second pipe, for taking filtrated fluid from the above-mentioned pump out to the exterior of the above-mentioned tank; and a third pipe for taking filtrated fluid out of the above-mentioned tank and a fourth pipe for returning filtrated fluid to the above-mentioned tank, which are branched, via an optical sensor, from the above-mentioned second pipe; and wherein during the process of forming the above-mentioned second filter, the above-mentioned fluid is circulated along a path running from the above-mentioned filtration unit to the above-mentioned first pipe, the above-mentioned pump, the above-mentioned second pipe, the above-mentioned optical sensor, and the above-mentioned fourth pipe.
The present invention is furthermore aimed at providing a filtration device, wherein the suction pressure of the above-mentioned pump during formation of the above-mentioned second filter is set lower than the suction pressure during filtration to form the above-mentioned second filter gently and keep the filtration flow rate fixed during formation of the above-mentioned second filter and during filtration.
The present invention is furthermore aimed at providing a filtration device, wherein the suction pressure of the above-mentioned pump during formation of the above-mentioned second filter is set lower than the suction pressure during filtration to form the above-mentioned second filter gently and keep the suction pressure fixed during formation of the above-mentioned second filter and during filtration.
The present invention is furthermore aimed at providing a filtration device, wherein switching from the above-mentioned fourth pipe to the above-mentioned third pipe is carried out to transfer to the filtration process when the optical transmittance detected by the above-mentioned optical sensor becomes greater than or equal to a fixed value.
The present invention is furthermore aimed at providing a filtration device comprising: a tank containing a fluid with objects of removal in the form of a colloidal solution; a filtration unit, formed of a first filter, which is immersed inside the above-mentioned tank, and a second filter, comprising a gel film that is adsorbed onto the surface of the first filter; a pump, for suctioning the above-mentioned fluid via a first pipe connected to the above-mentioned filtration unit; a second pipe, for taking filtrated fluid from the above-mentioned pump out to the exterior of the above-mentioned tank; and a flow meter, inserted in the above-mentioned second pipe; and wherein in the process of filtering the above-mentioned fluid by the above-mentioned filtration unit, the suction pressure of the above-mentioned pump is increased so as to keep the filtration flow rate measured by the above-mentioned flow meter constant.
The present invention is furthermore aimed at providing a filtration device comprising: a tank containing a fluid with objects of removal in the form of a colloidal solution; a filtration unit, formed of a first filter, which is immersed inside the above-mentioned tank, and a second filter, comprising a gel film that is adsorbed onto the surface of the first filter; a pump, for suctioning the above-mentioned fluid via a first pipe connected to the above-mentioned filtration unit; a second pipe, for taking filtrated fluid from the above-mentioned pump out to the exterior of the above-mentioned tank; and an auxiliary tank, connected to the above-mentioned first pipe and collecting filtrated fluid; wherein when the above-mentioned second filter becomes clogged and the filtration flow rate decreases, the above-mentioned pump is stopped to eliminate the suction pressure applied to the above-mentioned filtration unit and the filtrated fluid collected in the above-mentioned auxiliary tank is made to flow in reverse via the above-mentioned first pipe to the above-mentioned filter to thereby apply hydrostatic pressure to the above-mentioned filtration unit from the interior, to cause the above-mentioned first filter to swell outwards, and to cause the gel that has become adsorbed onto the surface of the above-mentioned second filter to separate.
The present invention is furthermore aimed at providing a filtration device, wherein the above-mentioned hydrostatic pressure is determined by the difference in the liquid level of the above-mentioned auxiliary tank and that of the above-mentioned tank.
The present invention is furthermore aimed at providing a filtration device, wherein an aeration pipe is disposed at a bottom part of the above-mentioned tank and the amount of bubbles generated is increased in comparison to that during filtration.
The present invention is furthermore aimed at providing a filtration device, wherein when regeneration of the above-mentioned second filter is completed, the above-mentioned pump starts re-filtration of the above-mentioned fluid.
The present invention is furthermore aimed at providing a filtration device, wherein when the regeneration of the above-mentioned second filter is completed, the above-mentioned pump starts re-filtration of the above-mentioned fluid and the filtrated water is supplied to the above-mentioned auxiliary tank.
Generally, for eliminating particulate matter of 200 nm or less, such as the abrasive grains mixed in a CMP slurry, a filter film having pores smaller than the particulate matter is employed. However, with the present invention, a gel film, formed from the objects of removal, is used as the filter and the numerous gaps that form in the filter are used as paths for passage of fluid. Also with this invention, since the filter itself is a cluster of particulate matter of the objects to be removed, the objects to be removed that cause clogging can be separated from the filter, enabling the realization of maintenance of the filtration capacity. Furthermore with this invention, even when the gel film filter becomes clogged as a result of continued filtration, the filter can be regenerated to continue filtration and realize filtration over a long period of time.